The overall goal of these studies is to define the role of Schwann cell gap junctions in the development and regeneration of peripheral nerve. The primary hypothesis is that mature myelinating Schwann cells express Cx32 in the form of reflexive contacts between paranodal and Schmidt-Lantermann incisures of a single cell, whereas proliferating Schwann cells in early development and distal to the site of nerve injury express another gap junction protein (CxS) that participates in intercellular coupling. Because point mutations in Cx32 are responsible for the X-linked form of Charcot-Marie-Tooth syndrome (CMTX), a demyelinating peripheral neuropathy, we will correlate changes in Cx32 expression with myelination in vivo and in culture. Because CxS expression and the proliferating phenotype are induced by nerve injury, we will examine the time course of changes after injury and effects on cultured cells of cytokines/growth factors to which Schwann cells are exposed after injury and during regeneration. We will apply a broadly based approach to these studies, taking advantage of recently developed animal models deficient in Cx32 and myelin proteins. Specific Aim 1. Identify the connexins present in rodent nerve and determine developmental changes in expression and distribution of connexins and correlate with changes in major myelin proteins. Specific Aim 2. Test the hypothesis that changes in connexin expression occur in peripheral nerve in response to various types of injury and in murine models of demyelinating disease. Specific Aim 3. Test the hypothesis that mitogens released during or following nerve injury induce changes in connexin expression and function in cultured Schwann cells. Specific Aim 4. Test the hypothesis that expression of gap junctions between Schwann cells during myelination in vivo will mimic developmental and regeneration changes in vivo. Together, the studies proposed in this application should greatly extend our knowledge of the cell biology of the Schwann cell and its modulation in pathological conditions.